The present invention is generally directed to processes, and more specifically to processes for improving the life of known magnetic brush cleaners, and/or to processes which extend the usability of magnetic brush carrier cleaners by adding toners containing negatively charging surface additives such as AEROSIL.RTM. and metal oxides, such as titanium oxides. In one embodiment of the present invention there is provided a process for extending the life of magnetic brush cleaners selected for imaging and printing methods, such as xerographic imaging and printing methods. In an embodiment of the present invention, there is provided a process for extending the life, for example from about 10,000 developed copies to about 40,000 copies, of magnetic brush cleaners selected for color imaging processes, such as trilevel imaging methods as illustrated herein by the coating and/or mixing of metal oxides directly with the magnetic brush cleaner carrier particles, and/or by blending the metal oxides with the input or added toner material such that the metal oxides become mixed with the carrier particles selected for the magnetic brush cleaner when, for example, the untransferred toner from an imaging member is removed by the magnetic brush cleaner carrier and subsequently transported through the cleaner housing to the waste toner sump. Magnetic brush processes and components are known, reference for example the Xerox Corporation 1075.TM. and 1090.TM. imaging apparatuses.
The process of charging a photoresponsive imaging member to a single polarity and creating on it an image of at least three different levels, a trilevel imaging process to which the present invention is applicable, of a potential of the same polarity is described in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference. This patent discloses a method of creating two colored images by creating on an imaging surface a charge pattern including an area of first charge as a background area, a second area of greater voltage than the first area, and a third area of lesser voltage than the first area with the second and third areas functioning as image areas. The charge pattern is developed in a first step with positively charged toner particles of a first color and, in a subsequent development step, developed with negatively charged toner particles of a second color. Alternatively, charge patterns may be developed with a dry developer containing toners of two different colors in a single development step. Also of interest with respect to the trilevel process for generating images is U.S. Pat. No. 4,686,163, the disclosure of which is totally incorporated herein by reference.
The photoresponsive imaging member can be negatively charged, positively charged, or both, and the latent image formed on the surface may be comprised of either a positive or a negative potential, or both. In one embodiment, the image comprises three distinct levels of potential, all being of the same polarity. The levels of potential should be well differentiated, such that they are separated by at least 100 volts, and preferably 200 volts or more. For example, a latent image on an imaging member can comprise areas of potential at -800, -400, and -100 volts. In addition, the levels of potential may comprise ranges of potential. For example, a latent image may be comprised of a high level of potential ranging from about -500 to about -800 volts, an intermediate level of potential of about -400 volts, and a low level ranging from about -100 to about -300 volts. An image having levels of potential that range over a broad area may be created such that gray areas of one color are developed in the high range and gray areas of another color are developed in the low range with 100 volts of potential separating the high and low ranges and constituting the intermediate, undeveloped range. In this situation, from 0 to about 100 volts may separate the high level of potential from the intermediate level of potential, and from 0 to about 100 volts may separate the intermediate level of potential from the low level of potential. When a known layered organic photoreceptor is employed, preferred potential ranges are from about -700 to about -850 volts for the high level of potential, from about -350 to about -450 volts for the intermediate level of potential, and from about -100 to about -180 volts for the low level of potential. These values can differ depending upon the type of imaging member selected.
Toner compositions with colored pigments are known. For example there is disclosed in U.S. Pat. No. 4,948,686, the disclosure of which is totally incorporated herein by reference, a process for the formation of two color images with a colored developer comprised of a first toner comprised of certain resin particles, such as styrene butadiene, a first pigment such as copper phthalocyanine, a charge control additive, colloidal silica and metal salts of fatty acid external surface additives, and a first carrier comprised of a steel core with, for example, a polymethyl methacrylate overcoating containing known conductive particles of, for example, carbon black, such as BLACK PEARLS.TM. carbon blacks available from Columbian Chemicals, present in an effective amount of, for example, from about 1 to about 40 weight percent of the coating, and wherein the coating weight is, for example, from about 0.2 to about 4 weight percent; and a second developer comprised of a black toner, a second charge additive and a steel core carrier with certain polymeric overcoatings, see claim 1 for example. Examples of colored toner pigments are illustrated in column 9, lines 10 to 26, and examples of charge additives for the toner are detailed in column 9, lines 27 to 43, of the aforementioned patent. For the black toner there can be selected the components as recited in columns 10 and 11, including charge additives such as distearyl dimethyl ammonium methyl sulfate, see column 11, lines 16 to 32. More specifically, there is illustrated in the 4,948,686 patent a process for forming two-color images which comprises, for example, (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by conductive magnetic brush development with a developer comprising a colored first toner comprising a first resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a first pigment present in an amount of from about 1 to about 15 percent by weight and selected from the group consisting of copper phthalocyanine pigments, quinacridone pigments, azo pigments, rhodamine pigments, and mixtures thereof; a charge control agent present in an amount of from about 0.2 to about 5 percent by weight; colloidal silica surface external additives present in an amount of from about 0.1 to about 2 percent by weight; and external additives comprising metal salts or metal salts of fatty acids present in an amount of from about 0.1 to about 2 percent by weight; and a first carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of a methyl terpolymer, polymethyl methacrylate, and a blend of from about 35 to about 65 percent by weight of polymethylmethacrylate and from about 35 to about 65 percent by weight of chlorotrifluoroethylene-vinyl chloride copolymer, wherein the coating contains from 0 to about 40 percent by weight of the coating of conductive particles and wherein the coating weight is from about 0.2 to about 3 percent by weight of the carrier; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a black second toner comprising a second resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a second pigment present in an amount of from about 1 to about 15 percent by weight; and a second charge control additive present in an amount of from about 0.1 to about 6 percent by weight; and a second carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of a chlorotrifluoroethylene-vinyl chloride copolymer containing from 0 to about 40 percent by weight of conductive particles at a coating weight of from about 0.4 to about 1.5 percent by weight of the carrier; polyvinylfluoride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and polyvinylchloride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and (5) transferring the developed two-color image to a substrate. Imaging members suitable for use with the above process may be of any type capable of maintaining three distinct levels of potential. Generally, various dielectric or photoconductive insulating material suitable for use in xerographic, ionographic, or other electrophotographic processes may be selected for the above process, and suitable photoreceptor materials include amorphous silicon, layered organic materials as disclosed in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, and the like.
Processes for obtaining electrophotographic, including xerographic, and two-colored images, and the like are known, reference for example U.S. Pat. Nos. 4,264,185; 4,308,821; 4,378,415; 4,430,402; 4,594,302; 4,500,616; 4,524,117; 4,525,447; 4,562,129 and 4,640,883, the disclosures of which are each totally incorporated herein by reference. In the '883 patent there is illustrated, for example, a method of forming composite or dichromatic images which comprises forming on an imaging member electrostatic latent images having at least three different potential levels, the first and second latent images being represented, respectively, by a first potential and a second potential relative to a common background potential. The first and second images are developed by a first magnetic brush using two kinds of toners, at least one of which is magnetic, and both of which are chargeable to polarities opposite to each other with application to a developing electrode of a bias voltage capable of depositing the magnetic toner on the background potential area to deposit selectively the two toners on the first and second latent images and to deposit the magnetic toner on the background potential area, while collecting the deposited magnetic toner at least from the background potential area by second magnetic brush developing means.
In a patentability search report the following U.S. patents are recited: U.S. Pat. Nos. 4,155,883 which discloses a toner with a certain thermoplastic resin binder, see the Abstract; also disclosed is a curing reaction between the toner body powder and a micropowder, wherein the micropowder is formed of TiO.sub.2, and the like, see column 2, line 67, and note the advantages in column 3; 4,623,605, which discloses a developer with a positive charge type carrier and a negative charge type toner, which toner can contain hydrophobic titanium oxide, see the Abstract; also see column 1, especially line 57, to column 3, especially lines 2 to 50; 4,647,522 which discloses a toner with oxide particles, such as titanium oxides, see the Abstract; also see column 1, especially line 55, and column 2, especially lines 1 to 30; 4,652,509, which discloses a toner with a hydrophobic titanium oxide; also, see column 2 for example; and 4,804,609, which discloses a developer with SiO.sub.2 and/or magnetite for the primary purpose of removing talc from copy paper sheets, see column 2 for example.
Moreover, illustrated in U.S. Pat. No. 5,075,185, the disclosure of which is totally incorporated herein by reference, are developers, toners and trilevel imaging processes thereof. In an embodiment of the '185 patent, there is provided a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by, for example, conductive magnetic brush development with a developer comprising carrier particles, and a colored first toner comprised of resin particles, colored, other than black, pigment particles, and an aluminum complex charge enhancing additive; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a second black developer comprised of carrier particles and a toner comprised of resin, black pigment, such as carbon black, and a charge enhancing additive; (5) transferring the developed two-color image to a suitable substrate; and (6) fixing the image thereto. In an embodiment of the aforementioned patent, the first developer comprises, for example, a first toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, PLIOLITES.RTM., crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; a first colored blue, especially PV Fast Blue pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 5 to about 10 weight percent; an aluminum complex charge enhancing additive; and a second developer comprised of a second toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polysters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, PLIOLITES.RTM., crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; and a black pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 1 to about 5 weight percent wherein the aforementioned black toner contains a charge enhancing additive such as an alkyl pyridinium halide, and preferably cetyl pyridinium chloride, and in an embodiment the black toner is comprised of 92 percent by weight of a styrene n-butyl methacrylate copolymer (58/42), 6 percent by weight of REGAL 330.RTM. carbon black, and 2 percent by weight of the charge enhancing additive cetyl pyridinium chloride.
Illustrated in U.S. Pat. No. 5,087,538, the disclosure of which is totally incorporated herein by reference, is a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by, for example, conductive magnetic brush development with a developer comprising carrier particles, and a colored first toner comprised of resin, a positively charging pigment, and a negatively charging pigment; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a second developer comprised of carrier particles and a toner comprised of resin, black pigment, such as carbon black, and a charge enhancing additive; (5) transferring the developed two-color image to a suitable substrate; and (6) fixing the image thereto.
A magnetic brush cleaner illustrated herein and applicable to the process of the present invention in embodiments is disclosed in U.S. Pat. No. 3,580,673, the disclosure of which is totally incorporated herein by reference, which brush is designed to remove residual toner from an imaging member after the image has been transferred to paper. The major components of the magnetic brush cleaner are the cleaner roll and detone roll with a scraper. The cleaner roll is comprised of a thin shell aluminum outer roll rotating about a stationary magnet assembly. The outer roll is covered by a conductive carrier material that brushes against the imaging member. The cleaner roll is typically biased to about -170 volts so as to attract and remove positively charged residual toner from the surface of the imaging member by electrostatic forces. A detone roll rotates against the cleaner roll and is typically biased to about -320 volts so that toner is transferred from the carrier particles on the cleaner roll to the detone roll. The scraper mechanically removes toner from the detone roll. When the cleaner roll carrier particles are comprised, for example, of 0.175 percent of polyvinylidene fluoride polymer coated on Hoeganaes steel core the color developers of the present invention promote cleaning failure within 10,000 to 20,000 copies due to the buildup in the magnetic cleaning brush of input toner surface additives. The present invention extends the magnetic brush cleaner lifetime for the development and cleaning conditions described herein by about 30,000 copies in embodiments by mixing selected metal oxides with the cleaner carrier so as to obviate the deleterious effects of such additive accumulation.